Flavonoids

Flavonoids (wiki)

Biological effects

Flavonoids are widely distributed in plants fulfilling many functions including producing yellow or red/blue pigmentation in flowers and protection from attack by microbes and insects.

Flavonoids have been referred to as "nature's biological response modifiers" because of strong experimental evidence of their inherent ability to modify the body's reaction to allergens, viruses, and carcinogens. They show anti-allergic, anti-inflammatory^[1] , anti-microbial and anti-cancer activity. In addition, flavonoids act as powerful antioxidants, protecting against oxidative and free radical damage.

Consumers and food manufacturers have become interested in flavonoids for their medicinal properties, especially their potential role in the prevention of cancers and cardiovascular disease. The beneficial effects of fruit, vegetables, and tea or even red wine have been attributed to flavonoid compounds rather than to known nutrients and vitamins.

Good sources of flavonoids include all citrus fruits, berries, onions, parsley, legumes, green tea, red wine, seabuckthorn, and dark chocolate (that with a cocoa content of seventy percent or greater).

Citrus

The citrus bioflavonoids include hesperidin, quercetin, rutin (a sugar of quercetin), and tangeritin. In addition to possessing antioxidant activity and an ability to increase intracellular levels of vitamin C, rutin and hesperidin exert beneficial effects on capillary permeability and blood flow. They also exhibit some of the anti-allergy and anti-inflammatory benefits of quercetin. Quercetin can also inhibit reverse transcriptase, part of the replication process of retroviruses (Spedding et al. 1989). The therapeutical relevance of this inhibition has not been established. Hydroxyethylrutosides (HER) have been used in the treatment of capillary permeability, easy bruising, hemorrhoids, and varicose veins.

Green Tea

Green tea polyphenols are potent antioxidant compounds that have demonstrated greater antioxidant protection than vitamins C and E. Green tea may also increase the activity of antioxidant enzymes. Green tea polyphenols may inhibit cancer by blocking the formation of cancer-causing compounds and suppressing the activation of carcinogens. The major polyphenols in green tea are flavonoids (catechin, epicatechin, epicatechin gallate, epigallocatechin gallate(EGCG), and proanthocyanidins).

Though both green tea and black tea are derived from the same plant (Camellia sinensis), they possess different antioxidants. In producing black tea the leaves are allowed to oxidize, during which enzymes present in the tea convert many polyphenols to larger molecules with different biological effects. However, green tea is produced by lightly steaming the fresh-cut leaf, which inactivates these enzymes, and oxidation does not occur.

Eat more fruit and vegetables

Scientific studies have shown that people who eat a lot of fruit and vegetables may have a lower risk of getting illnesses, such as heart disease and some cancers. For this reason, health authorities recommend that you eat at least five portions of fruit and vegetables every day - and it doesn't matter whether they're fresh, tinned, frozen, cooked, juiced or dried.

How much is a portion?

• One piece of medium-sized fruit - eg, an apple, peach, banana or orange.
• One slice of large fruit, such as melon, mango or pineapple.
• One handful of grapes or two handfuls of cherries or berry fruits.
• One tablespoon of dried fruit.
• A glass (roughly 100ml) of fruit or vegetable juice.
• A small tin (roughly 200g) of fruit.
• A side salad.
• A serving (roughly 100g) of vegetables - eg, frozen or mushy peas, boiled carrots or stir-fried broccoli.
• The vegetables served in a portion of vegetable curry, lasagne, stir-fry or casserole.

At least five portions of fruit and vegetables a day can reduce the risk of many different types of cancer. The exact reason for this is unknown, but it may be related to their:-

• fibre content
• vitamins and minerals
• other plant chemicals such as flavonoids,
  
• or the combination of all these nutrients.
  

Vitamin and mineral supplements may be a useful addition to the diet for some people, but they aren't a substitute for fresh fruit and vegetables

Vitamins

Eating a wide variety of fruit and vegetables means you're more likely to get all the vitamins and minerals you need. But what are vitamins - and why are they so important to your good health?

• Vitamins are organic substances - this means they're found in plants and animals.
• Most vitamins can't be made by your body, so they must be sourced from your diet. Vitamin D and the B vitamin niacin are exceptions to this.
• Nutritionists have divided vitamins into two groups: fat-soluble and water-soluble.
• The fat-soluble vitamins - A, D, E and K - are transported through your body by fat. They can also be stored in your fat and liver cells for a limited period of time.
• The water-soluble vitamins - B and C - are absorbed by and transported through your body in water. They need to be eaten every day, as you can't store them for any length of time.

Fat-soluble vitamins

Vitamin	Why important?	Where found?	Daily Recommendation
Vitamin A	It looks after your eyes, the lining of your nose, throat and lungs, and your skin cells.	Carrots, sweet potatoes, pumpkins, red chillies, tomatoes, 'orange' fruits, such as apricots and mango, and dark green leafy vegetables.	600µg for females, 700µg for males.
Vitamin D	It helps your body to absorb calcium, needed to ensure strong bones and teeth.	The most important source is the sun, but it's also found in tiny amounts in dairy products, cod liver oil and oily fish.	No recommendations as sunlight is the main source.
Vitamin E	It fights free radicals - unbalanced molecules that can cause damage to your cells. It also contributes to the healthy condition of your skin.	Vegetables, poultry, fish, fortified breakfast cereals, vegetable oils, nuts and seeds.	Up to 4mg for adult males and up to 3mg for adult females is considered a safe intake.
Vitamin K	It helps your body to make a number of proteins, one of which helps your blood to clot.	Dark green leafy vegetables such as Brussels sprouts, broccoli, cabbage, spinach and asparagus. It's also found in soya oil and margarine.	1µg for every kg of body weight is considered a safe intake for both men and women.

Water-soluble vitamins

Vitamin	Why important?	Where found?	Daily recommendation
B-complex Vitamins	They help you to metabolise your food and help your blood cells to form and flow.	Green vegetables, wholegrains, meat, such as liver, kidneys, pork, beef and lamb, vegetable extracts, nuts and fortified breakfast cereals.	Eight vitamins make up the B-complex family: B1 (Thiamin) - Adult male, 0.9mg. Adult female, 0.8mg. B2 (Riboflavin - Adult male, 1.3mg. Adult female, 1.1mg. B3 (Niacin) - Adult male, 17mg. Adult female, 13mg. B5 (Pantothenic Acid) - 3 to 7mg is considered a safe intake for both sexes. B6 (Pyridoxine) - Adult male, 1.4mg. Adult female, 1.2mg. B9 (Folate) - 200 mcg for both adult males and females. B12 (Cobalamin) - 1.5 µg for both adult males and females. Biotin - 10-20 µg is considered a safe intake for both sexes.
Vitamin C	It helps your body to produce collagen (important for skin and bone structure) and to absorb iron.	A wide variety of vegetables and fruit, including spinach, broccoli, tomatoes, strawberries, citrus fruit and potatoes.	40mg for both adult male and female.

Minerals

Vitamins aren't the only nutrients to be gained from fruit and vegetables. Minerals also have an important role to play in your good health.

• Minerals are inorganic substances. This means they're found in the rocks and soil.
• Vegetables absorb mineral goodness as they grow, while animals digest it through their diet.
• Like vitamins, minerals can also be divided into two groups - those that are needed in minute quantities and those that are needed in larger quantities.
• Minerals needed in larger amounts - the major minerals - include calcium, magnesium, sodium, potassium and phosphorus.
• Minerals needed in tiny amounts are called trace minerals. This group includes iron, zinc, iodine, selenium and copper.

Major minerals

Mineral	Why important?	Where found?	Daily recommendation
Calcium	It's essential for healthy bones and teeth.	It's in abundance in milk and dairy products. Very small quantities can be found in dark green leafy vegetables, such as spinach and watercress.	700mg for males and females.
Phosphorous	It contributes to healthy cells, bones and teeth.	You'll find it in milk, cheese, fish, meat and eggs.	550mg for males and females.
Magnesium	It helps your body to use energy and your muscles to function effectively.	Dark green leafy vegetables, such as cabbage and broccoli.	300mg for males and females.
Sodium	It helps your body to regulate its water content and your nerves to function effectively.	As table salt, added to food for flavour.	1,600mg for males and females.
Potassium	It helps your cells and body fluids to function properly.	In most foods, apart from fats, oil and sugar.	3,500mg for males and females.

Trace minerals

Mineral	Why important?	Where found?	Daily recommendation
Iron	It helps in the formation of red blood cells; deficiency can lead to anaemia.	Red meat, fortified cereals and bread, some fruit and vegetables.	8.7mg for males. 14.8 for females, but more if you experience a heavy menstrual flow.
Zinc	It helps the body to reach sexual maturity and aids the repair of damaged tissue.	Meat, fish, milk, cheese and eggs.	9.5mg for males. 7mg for females.
Copper	It helps your body to use iron properly.	Green vegetables and fish.	1.2mg for both males and females.
Selenium	It ensures healthy cells.	Meat, fish, cereals, eggs and cheese.	75µg for males. 60µg for females.
Iodine	It helps to make thyroid hormones, which control metabolic activity.	Seafood and dairy products.	140µg for both males and females.

From Wiki

Diffuse sky radiation is solar radiation reaching the earth's surface after having been scattered from the direct solar beam by molecules or suspensoids in the atmosphere. Also called skylight, diffuse skylight, or sky radiation. Of the total light removed from the direct solar beam by scattering in the atmosphere (approximately 25 percent of the incident radiation), about two-thirds ultimately reaches the earth as diffuse sky radiation.

Scattering is the process by which small particles suspended in a medium of a different index of refraction redirect a portion of the incident radiation in all directions. In elastic scattering, no energy transformation results, only a change in the spatial distribution of the radiation. The science of optics usually uses the term to refer to the deflection of photons that occurs when they are absorbed and re-emitted by atoms or molecules.

Why is the sky blue?

Clear blue sky.

The sky is blue partly because air scatters short-wavelength light in preference to longer wavelengths. Combined, these effects scatter (bend away in all directions) some short, blue light waves while allowing almost all longer, red light waves to pass straight through. When we look toward a part of the sky not near the sun, the blue color we see is blue light waves scattered down toward us from the white sunlight passing through the air overhead. Near sunrise and sunset, most of the light we see comes in nearly tangent to the Earth's surface, so that the light's path through the atmosphere is so long that much of the blue and even yellow light is scattered out, leaving the sun rays and the clouds it illuminates red.

Scattering and absorption are major causes of the attenuation of radiation by the atmosphere. Scattering varies as a function of the ratio of the particle diameter to the wavelength of the radiation. When this ratio is less than about one-tenth, Rayleigh scattering occurs in which the scattering coefficient varies inversely as the fourth power of the wavelength. At larger values of the ratio of particle diameter to wavelength, the scattering varies in a complex fashion described, for spherical particles, by the Mie theory; at a ratio of the order of 10, the laws of geometric optics begin to apply.

Why is the sky blue instead of violet?

Normalized typical human cone responses (and the rod response) to monochromatic spectral stimuli

Because of the strong wavelength dependence (inverse fourth power) of light scattering according to Raleigh's Law, one would expect that the sky would appear more violet than blue, the former having a shorter wavelength than the latter. There is a simple physiological explanation for this apparent conundrum. Simply put, the human eye cannot detect violet light in presence of light with longer wavelengths. There is a reason for this. It turns out that the human eye's high resolution color-detection system is made of proteins and chromophores (which together make up photoreceptor cells or "Cone" structures in the eye's fovea) that are sensitive to different wavelengths in the visible spectrum (400 nm–700 nm). In fact, there are three major protein-chromophore sensors that have peak sensitivities to yellowish-green (564 nm), bluish-green (534 nm), and blue-violet (420 nm) light. The brain uses the different responses of these chromophores to interpret the spectrum of the light that reaches the retina.

When one experimentally plots the sensitivity curves for the three color sensors (identified here as long (L), middle (M), and short (S) wavelength), three roughly "bell-curve" distributions are seen to overlap one another and cover the visible spectrum. We depend on this overlap for color sensing to detect the entire spectrum of visible light. For example, monochromatic violet light at 400 nm mostly stimulates the S receptors, but also slightly stimulates the L and M receptors, with the L receptor having the stronger response. This combination of stimuli is interpreted by the brain as violet. Monochromatic blue light, on the other hand, stimulates the M receptor more than the L receptor. Skylight is not monochromatic; it contains a mixture of light covering much of the spectrum. The combination of strong violet light with weaker blue and even weaker green and yellow strongly stimulates the S receptor, and stimulates the M receptor more than the L receptor. As a result, this mixture of wavelengths is perceived by the brain as blue rather than violet.

Neutral points

There are three commonly detectable points of zero polarization of diffuse sky radiation (known as neutral points) lying along the vertical circle through the sun.

• The Arago point, named for its discoverer, is customarily located at about 20° above the antisolar point; but it lies at higher altitudes in turbid air. The latter property makes the Arago distance a useful measure of atmospheric turbidity.

• The Babinet point, discovered by Babinet in 1840, typically lies only 15° to 20° above the sun, and hence is difficult to observe because of solar glare.

• The Brewster point, discovered by Brewster in 1840, is located about 15° to 20° directly below the sun; hence it is difficult to observe because of the glare of the sun.

Under an overcast sky

There is essentially zero direct sunlight under an overcast sky, so all light is then diffuse sky radiation. The flux of light is not very wavelength dependent because the cloud droplets are larger than the light's wavelength and scatter all colors approximately equally. The light passes through the translucent clouds in a manner similar to frosted glass. The intensity ranges (roughly) from 1/6 of direct sunlight for relatively thin clouds down to 1/1000 of direct sunlight under the extreme of thickest storm clouds.

See also

• Nighttime airglow
• Aerial perspective
• Daylight
• List of light sources

External links

• Why is the sky blue?
• Why is the sky blue?

Books

• Pesic, Peter (2005). Sky in a Bottle. The MIT Press. ISBN 978-0-262-16234-0.

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[Physics FAQ] - [Copyright]

Original by Philip Gibbs May 1997.

Why is the sky blue?

A clear cloudless day-time sky is blue because molecules in the air scatter blue light from the sun more than they scatter red light. When we look towards the sun at sunset, we see red and orange colours because the blue light has been scattered out and away from the line of sight.

The white light from the sun is a mixture of all colours of the rainbow. This was demonstrated by Isaac Newton, who used a prism to separate the different colours and so form a spectrum. The colours of light are distinguished by their different wavelengths. The visible part of the spectrum ranges from red light with a wavelength of about 720 nm, to violet with a wavelength of about 380 nm, with orange, yellow, green, blue and indigo between. The three different types of colour receptors in the retina of the human eye respond most strongly to red, green and blue wavelengths, giving us our colour vision.

Tyndall Effect

The first steps towards correctly explaining the colour of the sky were taken by John Tyndall in 1859. He discovered that when light passes through a clear fluid holding small particles in suspension, the shorter blue wavelengths are scattered more strongly than the red. This can be demonstrated by shining a beam of white light through a tank of water with a little milk or soap mixed in. From the side, the beam can be seen by the blue light it scatters; but the light seen directly from the end is reddened after it has passed through the tank. The scattered light can also be shown to be polarised using a filter of polarised light, just as the sky appears a deeper blue through polaroid sun glasses.

This is most correctly called the Tyndall effect, but it is more commonly known to physicists as Rayleigh scattering--after Lord Rayleigh, who studied it in more detail a few years later. He showed that the amount of light scattered is inversely proportional to the fourth power of wavelength for sufficiently small particles. It follows that blue light is scattered more than red light by a factor of (700/400)⁴ ~= 10.

Dust or Molecules?

Tyndall and Rayleigh thought that the blue colour of the sky must be due to small particles of dust and droplets of water vapour in the atmosphere. Even today, people sometimes incorrectly say that this is the case. Later scientists realised that if this were true, there would be more variation of sky colour with humidity or haze conditions than was actually observed, so they supposed correctly that the molecules of oxygen and nitrogen in the air are sufficient to account for the scattering. The case was finally settled by Einstein in 1911, who calculated the detailed formula for the scattering of light from molecules; and this was found to be in agreement with experiment. He was even able to use the calculation as a further verification of Avogadro's number when compared with observation. The molecules are able to scatter light because the electromagnetic field of the light waves induces electric dipole moments in the molecules.

Why not violet?

If shorter wavelengths are scattered most strongly, then there is a puzzle as to why the sky does not appear violet, the colour with the shortest visible wavelength. The spectrum of light emission from the sun is not constant at all wavelengths, and additionally is absorbed by the high atmosphere, so there is less violet in the light. Our eyes are also less sensitive to violet. That's part of the answer; yet a rainbow shows that there remains a significant amount of visible light coloured indigo and violet beyond the blue. The rest of the answer to this puzzle lies in the way our vision works. We have three types of colour receptors, or cones, in our retina. They are called red, blue and green because they respond most strongly to light at those wavelengths. As they are stimulated in different proportions, our visual system constructs the colours we see.

Response curves for the three types of cone in the human eye

When we look up at the sky, the red cones respond to the small amount of scattered red light, but also less strongly to orange and yellow wavelengths. The green cones respond to yellow and the more strongly-scattered green and green-blue wavelengths. The blue cones are stimulated by colours near blue wavelengths which are very strongly scattered. If there were no indigo and violet in the spectrum, the sky would appear blue with a slight green tinge. However, the most strongly scattered indigo and violet wavelengths stimulate the red cones slightly as well as the blue, which is why these colours appear blue with an added red tinge. The net effect is that the red and green cones are stimulated about equally by the light from the sky, while the blue is stimulated more strongly. This combination accounts for the pale sky blue colour. It may not be a coincidence that our vision is adjusted to see the sky as a pure hue. We have evolved to fit in with our environment; and the ability to separate natural colours most clearly is probably a survival advantage.

A multi-coloured sunset over the Firth of Forth in Scotland.

Sunsets

When the air is clear the sunset will appear yellow, because the light from the sun has passed a long distance through air and some of the blue light has been scattered away. If the air is polluted with small particles, natural or otherwise, the sunset will be more red. Sunsets over the sea may also be orange, due to salt particles in the air, which are effective Tyndall scatterers. The sky around the sun is seen reddened, as well as the light coming directly from the sun. This is because all light is scattered relatively well through small angles--but blue light is then more likely to be scattered twice or more over the greater distances, leaving the yellow, red and orange colours.

A blue haze over the mountains of Les Vosges in France.

Blue Haze and Blue Moon

Clouds and dust haze appear white because they consist of particles larger than the wavelengths of light, which scatter all wavelengths equally (Mie scattering). But sometimes there might be other particles in the air that are much smaller. Some mountainous regions are famous for their blue haze. Aerosols of terpenes from the vegetation react with ozone in the atmosphere to form small particles about 200 nm across, and these particles scatter the blue light. A forest fire or volcanic eruption may occasionally fill the atmosphere with fine particles of 500-800 nm across, being the right size to scatter red light. This gives the opposite to the usual Tyndall effect, and may cause the moon to have a blue tinge since the red light has been scattered out. This is a very rare phenomenon--occurring literally once in a blue moon.

Opalescence

The Tyndall effect is responsible for some other blue coloration's in nature: such as blue eyes, the opalescence of some gem stones, and the colour in the blue jay's wing. The colours can vary according to the size of the scattering particles. When a fluid is near its critical temperature and pressure, tiny density fluctuations are responsible for a blue coloration known as critical opalescence. People have also copied these natural effects by making ornamental glasses impregnated with particles, to give the glass a blue sheen. But not all blue colouring in nature is caused by scattering. Light under the sea is blue because water absorbs longer wavelength of light through distances over about 20 metres. When viewed from the beach, the sea is also blue because it reflects the sky, of course. Some birds and butterflies get their blue colorations by diffraction effects.

Why is the Mars sky red?

Images sent back from the Viking Mars landers in 1977 and from Pathfinder in 1997 showed a red sky seen from the Martian surface. This was due to red iron-rich dusts thrown up in the dust storms occurring from time to time on Mars. The colour of the Mars sky will change according to weather conditions. It should be blue when there have been no recent storms, but it will be darker than the earth's daytime sky because of Mars' thinner atmosphere.

Body fat percentage (wiki)

Body fat percentage is the fraction of the total body mass that is adipose tissue, as opposed to lean body mass (muscle, bone, organ tissue, blood, and everything else). This index is often used as a means to monitor progress during a diet or as a measure of physical fitness for certain sports, such as body building. It is more accurate as a measure of excess body weight than body mass index (BMI) since it takes into account muscle mass and frame size. However, its popularity is less than BMI because most of the techniques used to measure body fat percentage require equipment and skills that are not readily available.

Total body fat percentage consists of essential fat and storage fat. Essential fat is that amount necessary for maintenance of life and reproductive functions. The percentage for women is greater than that for men, due to the demands of childbearing and other hormonal functions. Essential fat is 2-5% in men, and 10-13% in women. Storage fat consists of fat accumulation in adipose tissue, part of which protects internal organs in the chest and abdomen. Again, women have slightly more than men. The minimum recommended total body fat percentage exceeds the essential fat percentage value reported above.[1]

Recommendations

Some body fat percentage levels are more culturally valued than others, and some are related to better health or improved athletic performance.

According to Thomas A. Owens, M.D. (Departments of Internal Medicine and Pediatrics, Duke University Medical Center, Durham, NC), body fat percentage is categorized as follows:^[1] :

Description	Women	Men
Recommended amount	20-21%	13-17%
Adults in United States, average	22- 25%	17-19%
Obese	30%+	25%+

According to Health Check Systems^[2], The American Council on Exercise^[3] has categorized ranges of body fat percentages as follows:

Description	Women	Men
Essential fat	10-12%	2-4%
Athletes	14–20%	6–13%
Fitness	21–24%	14–17%
Acceptable	25–31%	18–25%
Obese	32%+	25%+

Measurement techniques

A person's exact body fat percentage generally cannot be determined, but there are several different ways we can estimate it, each with varying degrees of accuracy.

Dual energy X-ray absorptiometry

Dual energy X-ray absorptiometry, or DXA (formerly DEXA), is a good method for estimating body fat percentage.

There are several more complicated procedures that more accurately determine body fat percentage. Some, referred to as multicompartment models, can include DXA measurement of bone, plus independent measures of body water (using the dilution principle with isotopically labeled water) and body volume (either by water displacement or air plethsmography). Various other components may be independently measures, such as total body potassium.

In addition, the most refined method, in-vivo neutron activation, can quantify all the elements of the body and use mathematical relations among the measured elements in the different components of the body (fat, water, protein, etc.) to develop simultaneous equations to estimate total body composition, including body fat. This is the most accurate method. You can also use many other methods to calculate body fat percentage/

Body Average Density Measurement (Hydrostatic Weighing)

Prior to the adoption of DXA, the most accurate method of estimating body fat percentage was to weigh a person underwater in order to obtain the average density (mass per unit volume). Since fat tissue has a lower density than muscles and bones, it is possible to estimate the fat content. This estimate is distorted by the fact that muscles and bones have different densities: for a person with a more-than-average amount of bone tissue, the estimate will be too low. However, this method gives highly reproducible results for individual persons (± 1%), unlike the methods discussed below, which can have an error up to ±10%.^[5] The body fat percentage is commonly calculated from one of two formulas:

• Brozek formula: BF = (4.57/ρ − 4.142) × 100
• Siri formula is: BF = (4.95/ρ − 4.50) × 100

In these formulas, ρ is the body density in kg/L.

where ρ_w is the density of water [0.99780 kg/L at 22 °C (72 °F)]. For example, a person weighing 80 kg needs to hold a floater with a volume of 4.5 L and a mass of 0.5 kg has a density of 1.05 kg/L and hence a body fat percentage of 21%. Note that both the Brozek and Siri formulas are claimed to give systematically too high body fat percentages. ^[6]

Bioelectrical Impedance Analysis

The Bioelectrical impedance analysis (BIA) method is more affordable but less accurate way to estimate body fat percentage. The general principle behind BIA: two conductors are attached to a person's body and a small electrical charge is sent through the body. The resistance between the conductors will provide a measure of body fat, since the resistance to electricity varies between adipose, muscular and skeletal tissue. Criticism of this methodology is based on where the conductors are placed on the body; typically they are placed on the feet, with the current sent up one leg, across the abdomen and down the other leg. As men and women store fat differently around the abdomen and thigh region, the results can be less accurate as a measure of total body fat percentage. Another variable that can affect the amount of body fat this test measures is the amount of liquid an individual has consumed before the test. As electricity travels more easily through water, a person who has consumed a large amount of water before the test will measure as a lower body fat percentage. Less water will increase the percentage of body fat. Bioelectrical impedence analysis is available in a laboratory, or for home use in the form of body fat scales and hand held body fat analyzers.

Skinfold Measurements

A simpler procedure for estimating body fat is the skinfold test, whereby a pinch of skin is precisely measured by calipers at several standardized points on the body to determine the subcutaneous fat layer thickness. These measurements are converted to an estimated body fat percentage by an equation. It is of utmost importance to test in a precise location with a fixed pressure.

Girth Comparisons

There exist formulae for estimating body fat percentage from an individual's weight and girth measurements. For example, the U.S. Navy Circumference method compares abdomen or waist and hips measurements to neck measurement and height^[7], and other sites claim to estimate one's body fat percentage by a conversion from the body mass index. Unfortunately, these measures are usually inaccurate as a way of determining body composition.

External links

• A Guide to Body Fat Percentage
• Gallagher D, Heymsfield S, Heo M, Jebb S, Murgatroyd P, Sakamoto Y (2000). "Healthy percentage body fat ranges: an approach for developing guidelines based on body mass index.". Am J Clin Nutr 72 (3): 694-701. PMID 10966886.
• Body Composition
• Yuhasz Skinfold Test
• Fat Caliper Measurement Sites

Body Fat Percentage

Many fad diets, with little or no exercise can cause a person to lose as much muscle tissue as fat. What's more...

There is a good chance that this person will return to their pre-diet weight. Only now they gain back more fat and less lean muscle. Essentially , they are the same weight but they now have a higher body fat percentage and less lean muscle mass. The point to remember is...

Weighing scales will not show any of these changes. Measuring your body fat percentage will. Measure it and you can manage it. If you notice you are losing considerable lean tissue mass as well as fat, you can take appropriate steps to adjust your program.

Sam follows a proper exercise and nutrition program. After a month or so of dedication and determination she notices her weight has changed only slightly if at all... Arrgh!

Not getting discouraged Sam has her body fat percentage measured...

Before her program Sam weighed 150lbs with a body fat percentage of 30%. After 6 weeks she weighs 148lbs. But her body fat percentage has dropped to 26%. The result?

Over 6.5lbs of highly-motivating fat loss! And she has gained 4.5lbs of healthy lean muscle. This situation is so common that you should never gauge the success of a weight loss program with the bathroom scales alone.

And it's exactly the same for someone on weight gain program... only in reverse. In this case any additional weight should come from lean muscle mass. No way to tell that with the bathroom scales. Plus, what if you're weight stays the same? Maybe you put on 10lbs of muscle while losing 10lbs of fat.

So what other benefits does knowing your body fat percentage give you? Let's look at the long term picture and consider your...

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General Health and Well Being

It would be easy to slip into all the negative consequences of excess body fat here. But let's stay on a positive track...

Why is calculating your body fat percentage so crucial to general health and successful aging?

Studies are showing that a typical person living in the western world steadily loses muscle and gains fat starting at age 20. What does that mean exactly?

Well, even if this person maintains a steady weight throughout their life there's a good chance their body fat percentage is increasing and their lean tissue mass is decreasing.

Traditionally aging and all it's physical frailties was seen as inevitable. Not any more...

Most gerontologists agree that simple lifestyle changes can have a dramatic effect on the aging process. The loss of functional strength, increase in body fat percentage, decrease in bone density, reduction in flexibility and decline in aerobic power are all under our control.

Measure your body fat percentage regularly and many of the detrimental signs of old age won't quietly creep up on you.

You'll be able to see, first hand, the changes occurring in your body and, if you choose, you can do something about it.

Before we move on to optimum body fat percentages and the very best ways to measure it, there's one more area affected by your body fat percentage...

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Your Ideal Body Fat Percentage

The absolute perfect body fat percentage does NOT exist. Age and gender make a big contribution to the ideal value, but most importantly...

Everyone is an individual. Some people might feel and perform better at a higher or lower body fat percentage than others of the same age and sex. And that's why...

Ranges and guidelines exist. Have a look at the tables below. The first table gives the ideal body fat percentage ranges for the general population. The second table is the average body fat percentage for different athletes. The important thing to remember is...

Anywhere inside the range is good. Staying below the upper limit should be your target but as you'll soon see lower is not necessarily better.

Body Fat Percentage for The Average Population
Age	Up to 30	30-50	50+
Females	14-21%	15-23%	16-25%
Males	9-15%	11-17%	12-19%

>

Average Body Fat Percentage of Athletes
Sport	Male	Female	Sport	Male	Female
Baseball	12-15%	12-18%	Rowing	6-14%	12-18%
Basketball	6-12%	20-27%	Shot Putters	16-20%	20-28%
Body building	5-8%	10-15%	Skiing (X country)	7-12%	16-22%
Cycling	5-15%	15-20%	Sprinters	8-10%	12-20%
Football (Backs)	9-12%	No data	Swimming	9-12%	14-24%
Football (Linemen)	15-19%	No data	Tennis	12-16%	16-24%
Gymnastics	5-12%	10-16%	Triathlon	5-12%	10-15%
High/long Jumpers	7-12%	10-18%	Volleyball	11-14%	16-25%
Ice/field Hockey	8-15%	12-18%	Weightlifters	9-16%	No data
Racquetball	8-13%	15-22%	Wrestlers	5-16%	No data

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Lower is Not Necessarily Better

A certain amount of body fat is vital for the body to function normally and healthy. In fact striving for a body fat percentage that is too low can be dangerous. Here's why...

Measuring your body fat percentage calculates your TOTAL body fat. This total body fat can be split into 2 categories...

Storage Fat -- This consists mainly of fat deposited just under the skin or subcutaneous fat. Storage fat for men and women is fairly similar. For the average man 12% of bodyweight is storage fat and for the average woman 15% of bodyweight is storage fat.

Essential Body Fat -- For the body to function normally and healthily a certain amount of body fat is required. This is called essential fat. For women the average amount of essential fat is 12% of bodyweight and for men it is 3%.

Trying to achieve a body fat percentage that is so low it affects your essential fat stores is NOT good for your health.

Some storage fat is also required for good health. It's used to protect internal organs in the chest and abdomen. So remember...

Aim to stay within the range for age and gender and rest assured you are taking one of the most positive steps to life-long health you can.

Return to Body Fat Percentage Archive

Corby worst, Bristol best in 'yob map' of England

One in two people in Corby believe anti-social behaviour is a problem

The Northamptonshire town of Corby has been named the "yob" capital of England in a spending watchdog report.

The National Audit Office used official figures to assess residents' perceptions of anti-social behaviour.

Analysis of the data suggested 48.8% of adults in Corby believed bad behaviour was a problem.

The study also suggests 17% of the population across England thought there were high levels of anti-social behaviour in general.

As part of its report The Home Office: Tackling Anti-Social Behaviour, the National Audit Office (NAO) said the percentage of people who believed anti-social behaviour was a problem had risen from 16% two years ago.

The worst 10 towns and cities Corby 48.8 Mansfield 44.4 Hackney 42.7 Nottingham 42.7 Luton 42.7 Slough 42.0 Ashfield (Notts) 41.2 Knowsley (Merseyside) 39.2 Middlesbrough 39.3 Easington (Durham) 38.9 Percentage of adults who think anti-social behaviour is a problem

The survey of all English local authorities suggested almost one in two people believed so-called "yobbish" behaviour was a big or fairly big problem in Corby.

Bristol was named as the place with the fewest perceived anti-social problems with only 5.7% of residents describing it as a big or fairly big issue.

The best 10 Bristol 5.7 Staffordshire Moorlands 6.0 Basingstoke and Deane 7.4 Wolverhampton 7.5 Leeds 8.9 Winchester 9.6 Sevenoaks 9.9 City of London 10.2 Richmond upon Thames 10.6 Blaby 10.8

The report also suggested about 55% of anti-social behaviour orders had been breached.

The Asbos were either breached by offenders committing more offences or by breaking the terms of the order.

The NAO said 35% of Asbo holders breached the order on five or more occasions, but the average number was four per person.

The government said the findings did not mean Asbos were failing.

Scanner could reveal hidden fat

The scan can pinpoint the exact distribution of

A body scanner could help fitness fans work out exactly how much of their bodies are made up of fat.

Doctors could use the device - developed by UK scientists - to look for abnormal fat which may be putting their patients at risk.

Scientists at Lancaster University and the Institute of Food Research in Norwich used radiowaves to detect fat beneath the skin.

It is hoped that such machines could be commonplace in leisure centres one day.

The device works on the principle that the human body is a mixture of water and fat.

The amount of fat on a person can be calculated by working out their density using their exact volume and weight.

Other methods pass a tiny electrical current through the body - the level of resistance to the current can be used to estimate fat content.

However, none of these methods is particularly practical to be used in seriously-ill patients - or ordinary members of the public who need an easy way to find out the truth about their bodies.

Field method

The new method, revealed in New Scientist magazine, involves passing coils which create a radio-frequency electromagnetic field over the body.

The make-up of the object within the coil alters the phase of the field - and this can be measured and used to estimate the water content - and hence the fat content.

We should be able to put something like this in a leisure centre and members of the public could use it on a regular basis Dr Henri Tapp, Institute of Food Research

When this information is coupled with an exact measurement of the body's volume collected by four lasers sweeping across it, the researchers can in theory create a rough picture of not only the amount of fat, but also its location on the body.

Dr Henri Tapp, from the Institute of Food Research, told BBC News Online: "The technique is called magnetic induction tomography - it has been around for a while, but it is the first time it has been used this way.

While traditional measures of obesity, such as body mass index, can help doctors predict the risk of diseases such as diabetes or heart disease, there is increasing evidence that the precise location of that fat - whether it evenly distributed or located around the waist - also has a bearing.

'Fat scan' shows up health risk

Fat appears white on the MRI scan

A scan can spot which people harbour dangerous levels of fat around their vital internal organs, scientists say.

Hammersmith Hospital, in west London, is currently the only hospital in Europe using the MRI scan.

Its scientists say 40% of the population have "bad" fat around the heart, liver or pancreas, even though many appear thin. Only a litre of fat should surround these internal organs. People who are thin but do little exercise often exceed this amount.

They warn it is possible to be slim and yet still be at risk of conditions like diabetes because of "hidden" fat.

Evidence suggests the precise location of fat has more of a bearing on health than simply being overweight.

For example, people who have too much weight around their middle, often called an "apple" shape, have a greater risk of developing heart disease and type 2 diabetes than those who are pear shaped and carry the weight around the hips.

Fat is good in general, but when you have too much of it or fat in the wrong places it is bad Researcher Professor Jimmy Bell 'I'm fat on the inside'

While doctors can check whether a person is a healthy weight for their height by calculating their body mass index or BMI (weight in kilograms divided by height in metres squared), they cannot see the dangerous hidden fat.

Lead researcher Professor Jimmy Bell, a Medical Research Council scientist, explained: "One of the problems with BMI is it gives you the wrong idea of how much fat you have.

"It's about where you have the fat.

"Fat is good in general, but when you have too much of it or fat in the wrong places it is bad.

"Someone can look really thin and have a normal BMI but have seven litres of fat inside them when they should ideally only have one litre."

Once doctors are aware someone has dangerous levels of hidden fat, they can work out the right combination of exercise and healthy eating needed to shift it, Professor Bell said.

He explained: "We are trying to understand what factors - genetic and environmental - make people put on fat internally and then determine what people need to do to get rid of this fat.

"When you diet you don't lose the right type of fat. If you exercise you lose more of the bad fat.

"If people are only going to do an hour of exercise a week, let's make sure that hour is spent doing the right exercise to shift the important internal fat."

Scientific Method: Parsimonious - sparing in proposed explanations - Occam's Razor

One of the requirements of the Scientific Theory / Scientific Method is Parsimonious: sparing in proposed entities or explanations, see Occam's Razor

Occam's razor (also spelled Ockham's razor) is a principle attributed to the 14th-century English logician and Franciscan friar William of Ockham (Guilhelmi Ockam and Guillermi de Ockam in Latin [1]). Originally a tenet of the reductionist philosophy of nominalism, it is more often taken today as a heuristic maxim that advises economy, parsimony, or simplicity in scientific theories.

Occam's razor states that the explanation of any phenomenon should make as few assumptions as possible, eliminating, or "shaving off", those that make no difference in the observable predictions of the explanatory hypothesis or theory. In short, when given two equally valid explanations for a phenomenon, one should embrace the less complicated formulation. The principle is often expressed in Latin as the lex parsimoniae (law of succinctness):

entia non sunt multiplicanda praeter necessitatem,

which translates to:

entities should not be multiplied beyond necessity.

This is often paraphrased as "All things being equal, the simplest solution tends to be the best one." In other words, when multiple competing theories are equal in other respects, the principle recommends selecting the theory that introduces the fewest assumptions and postulates the fewest hypothetical entities. It is in this sense that Occam's razor is usually understood.

Karl Popper

Karl Popper argues that a preference for simple theories need not appeal to practical or aesthetic considerations. Our preference for simplicity may be justified by his falsifiability criterion: We prefer simpler theories to more complex ones "because their empirical content is greater; and because they are better testable" (Popper 1992). In other words, a simple theory applies to more cases than a more complex one, and is thus more easily refuted.

Science by Razor alone?

When it is proposed as a maxim of science, Occam's razor is construed as a decision procedure for choosing among competing systems of hypotheses. In this context a system of hypotheses, together with its supporting definitions and its logical consequences, is commonly described as a theory.

Occam's razor has become a basic tool for those who follow the scientific method. The primary activity of science — formulating theories and selecting the most promising ones — is impossible without a way of choosing from among the theories which fit the evidence equally well, the number of which can be arbitrarily large (see underdetermination).

Creationism creeps into UK schools

"The fact is that creationism, in all its guises, is no longer a quintessentially American problem," says Michael Zimmerman, the architect of The Clergy Letter Project, an alliance of Christians who back evolution.

E O Wilson might want to talk to The Clergy Letter Project. (source: Christopher Govan Street)

IN THE beginning there was the Discovery Institute in Seattle, Washington, the religious think tank that has backed the US "intelligent design" movement. And lo it came to pass that a group called Truth in Science appeared in the land of the Brit-ites.

Now, making what most see as a mockery of its name, Truth in Science has circulated material to UK schools aiming to counter the teaching of evolution in science classes. Some 59 schools in the UK are now using the information packs, which promote the notion that life on Earth was created through intelligent design, a euphemism for the biblical story of creation.

According to The Guardian newspaper in London, the packs include a manual and two DVDs and were sent on 18 September to all the country's secondary schools. "The fact is that creationism, in all its guises, is no longer a quintessentially American problem," says Michael Zimmerman, professor of liberal arts and sciences at Butler University in Indianapolis, Indiana, and the architect of The Clergy Letter Project, an alliance of Christians who back evolution.

“Creationism in all its guises is no longer a quintessentially American problem”

"It is spreading worldwide and has made significant inroads in the UK," says Zimmerman. "The best way to overcome this pernicious situation is for religious leaders and scientists to come together to discuss how religion and science can be compatible - how they use different methodologies to help people understand the world and the human condition," he says.

From issue 2580 of New Scientist magazine, 02 December 2006, page 4

Intelligent Design

Intelligent design (ID) is the concept that "certain features of the universe and of living things are best explained by an intelligent cause, not an undirected process such as natural selection."^[1][2][3] All of its leading proponents are affiliated with the Discovery Institute.^{[4][5][6][7][8][9]} They say that intelligent design is a scientific theory that stands on equal footing with, or is superior to, current scientific theories regarding the evolution and origin of life.^[10]

An overwhelming majority of the scientific community views intelligent design as unscientific,^[11] as pseudoscience^[12][13] or as junk science.^[14][15] The U.S. National Academy of Sciences has stated that intelligent design "and other claims of supernatural intervention in the origin of life" are not science because they cannot be tested by experiment, do not generate any predictions, and propose no new hypotheses of their own.^[16]

In Kitzmiller v. Dover Area School District (2005), a United States federal court ruled that a public school district requirement for science classes to teach that intelligent design is an alternative to evolution was a violation of the Establishment Clause of the First Amendment to the U.S. Constitution. United States District Judge John E. Jones III ruled that intelligent design is not science and is essentially religious in nature.^[17]

Scientific critique of creationism

Since the origins of modern geology in the 18th and 19th centuries, forms of creationism have become increasingly separated from mainstream science. As modern science called into question the literal interpretations of biblical account of creation in Genesis, creationists (especially Young Earth creationists) began to actively oppose the scientific consensus on questions of origins.

There is a fundamental difference between the scientific approach to explaining the natural world and the creationist approach. The scientific approach uses the scientific method as a means of discovering information about nature. Scientists use observations, hypotheses and deductions to propose explanations for natural phenomena in the form of scientific theories. Predictions from these theories are tested by experiment. If a prediction turns out to be correct, the theory survives. This is a meritocratic form of systematic enquiry, where the best ideas supported by evidence and positive experimental results survive. In principle, the scientific method does not seek answers that fit a certain pre-determined conclusion, but rather works to construct viable, testable, and provable theories based on a solid evidential foundation. The evidential foundation therefore precludes any reference to revelation.

Creationism, on the other hand, works by taking theologically conservative interpretations of scripture as the primary or only source of information about origins. Creationists believe that since the Creator created everything and also revealed scriptures, the scriptures have pre-eminence as a kind of evidence. Consistency with their interpretations of scripture is the measure by which they judge all other evidence. They then accept or reject scientific accounts based on whether or not they agree with their beliefs, discounting that which contradicts their understanding of scriptural revelation. This perspective can be seen as a type of luddism or anti-modernism since any seemingly opposing ideas are either ignored or dismissed. Those who oppose creationism point out that such positions are fundamentally unscientific and a hallmark of pseudoscience. Additionally, aspects of the scriptures which are not subject to scientific examination are not considered as reliable evidence to scientists.

Certain adherents to creationism have declared that there exist versions of creationism (namely creation science) that are based on the scientific method. It was such claims that were the basis for the legal arguments that creationism deserved equal-time in the science classroom. Skeptical critics charge that creation science is not a theory that has come about through a systematic and scientific accumulation of evidence. It is predominantly based on the assumption of a literal interpretation of religious scripture and the emphasis of the authority of scripture over other sources of knowledge is evident in creation science literature.

All scientific theories are falsifiable; that is, if evidence that contradicts any given theory comes to light, or if the theory is proven to no longer fit with the evidence, the theory itself is shown to be invalid and is either modified to be consistent with all the evidence or is discarded. Scientific theories can be (and often are) found to be incorrect or incomplete. Since creationism rests on an article of faith, its construction assumes that the narrative accounts of origins can never be shown falsified, no matter how strong the evidence is to the contrary.

Evolutionary modern synthesis is the theory that fits all known biological and genetic evidence while being backed up by overwhelming evidence in the fossil record. Contrary to frequent claims by many opponents of the theory of evolution, transitional fossils exist which show a gradual change from one species to another. Moreover, evolutionary selection has been observed in living species (for a macroscopic instance, “tuskless elephants,” see elephant).

In the last ten years, DNA analysis techniques applied to many organisms have demonstrated the genetic relationship between all forms of known life (humans share 50% of their DNA with yeast, 96 with chimpanzees). Even if the theory of evolution was disproved, this would not imply separate human creation, which is the main feature of creationism in the Abrahamic religions. It is exclusively in the public sphere, where young Earth creationists (especially in the U.S.) have fought for recognition of their world view, that the debate about creationism and evolution continues.